Material containing both a negative electric permittivity and magnetic permeability (at a given frequency) exhibit a negative index of refraction. These materials are referred to as left handed materials (LHM) or negative index materials (NIM) and have an ability to re-focus light passing through them. Scientific literature describing thin wires and split-ring resonators (SRRs) paved the way for the fabrication of metamaterials exhibiting negative index properties at microwave frequencies, Scientific literature has also disclosed the use of an array of thin metal wires to enable plasma frequency of a metal to be shifted predictably to microwave frequencies. Further, it has been disclosed that the permeability of a metamaterial can be made negative using an array of non-magnetic coupled metallic SRRs. This ability was demonstrated in the microwave range by D Smith, et. al., Phys, Rev. Lett., 84 4184 (2000), and more recently in the 100 terahertz range by Linden, in S. Linden, et. al., Science, 306, 1351 (2004). In these fixed frequency structures, the size and spacing of the individual components comprising the metamaterial were assumed much smaller than the wavelength of the resonant frequency of operation.
Smith's NIM structure used SRR and strip lines made of copper over circuit board material and were fount to be functional at single narrow band frequencies only. However, these structures demonstrated that microwave radiation passing through the wedged shaped NIM is bent through a large negative angle, obeying Snell's Law, n1*sin(θ1)=n2*sin(θ2). Since n2 is negative, sin(θ2) is also negative, which yields a large change in the angle.
Artificial effective media are attractive because of applications such as super lens and electromagnetic invisibility1,2. However, the inevitable loss due to a strong dispersive nature is one of the fundamental challenges preventing such applications from becoming reality. Recently, the discussions of incorporating active elements into artificial media to compensate loss and potentially bandwidth have attracted more and more interests3-12. However, controversies concerning causality of artificial active media persist.
Prior to the present invention, the theory of the impossibility of constructing an artificial material having a negative refractive index (NRI) and net gain13-18 was widely accepted. In optics, a diverse family of “gain media”, primarily based on doped crystalline, semiconductors, dyes and gases, have been widely used in laser technologies19-23. Simulations have shown that placing optical gain media (i.e., optically pumped laser dyes) in fishnet metamaterial cells results in optical “gain metamaterial” able to exhibit a NRI in a narrow bandwidth without violating causality4,7. The significance of this conception is, while this artificial gain medium still functions as a laser amplifier, it compensates (or, potentially over-compensates) for the intrinsic loss found in traditional metamaterials. This artificial gain medium inherits the theoretical superiorities of metamaterials, (i.e., the ability to provide arbitrarily controlled constitutive parameters not found in nature5). Thus, “gain metamaterials” have the realistic potential in implementing metamaterial applications (e.g. perfect lenses), where intrinsic losses fundamentally plague their realizations. However, although significant loss compensation for a fishnet metamaterial at optical frequency has been reported8, volumetric metamaterial with negative refractive index and gain has not been reported.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.